In a field of manufacturing a semiconductor device and a photomask or the like, it is frequently required that an unnecessary part of a resist film formed on a main surface of a substrate is removed. For example, when a resist film is applied on the substrate, by adopting a spin coating method for forming a uniform resist film on the substrate by dripping a coating liquid on a horizontally held substrate, and using a centrifugal force which is caused by rotating the substrate, a film thickness of a peripheral edge becomes large, because when the substrate is rotated at a low speed so that the coating film is uniformly formed on an entire surface of the substrate, the centrifugal force which acts on the peripheral edge of the substrate surface becomes smaller, whereby resist liquid remains on the peripheral edge of the substrate surface. When the film thickness becomes large as described above, whereby build-up of the peripheral edge of the substrate surface occurs, a problem is involved therein as described below.
Specifically, in a manufacturing step of the photomask blank, the substrate is kept by a transfer mechanism and is inserted in and pulled out from a substrate housing case, in a course passing through each kind of processing step after the resist is formed on the substrate surface. At this time, the peripheral edge of the substrate comes into contact with a chuck part of the transfer mechanism and a housing groove of the housing case, whereby the resist film of the peripheral edge of the substrate is released therefrom, to become a source of discharging dust, and the released resist adheres to the main surface of the photomask blank, and a defect is thereby generated.
Therefore, in order to avert the aforementioned situation, the substrate is subjected to spin-coating to form the resist film on the substrate, and thereafter the resist film on the peripheral edge of the substrate is removed. In the processing, a chemical liquid by which the resist is dissolved is fed to the resist on the peripheral edge of the substrate while rotating the substrate horizontally around a specified rotation center, and the resist film on the peripheral edge of the substrate is thereby dissolved and removed.
For example, a technique to remove the unnecessary resist film on the peripheral edge of the substrate includes a method disclosed in Japanese Patent Application No. 2001-259502.
The method of removing the unnecessary film comprises: forming the resist film by the spin-coating method, covering the surface of the substrate with a cover member formed with a plurality of fine holes on the peripheral edge of the substrate (part located in the upper part of the unnecessary film to be removed), and feeding the chemical liquid (solvent), by which the resist is dissolved, from above this cover member, while the substrate and the cover member are integrally rotated. The solvent thus fed is fed to the peripheral edge of the substrate through the fine holes, and the resist formed on the peripheral edge of the substrate is thereby dissolved and removed.
Note that an alignment mark and a QA (quality assurance) pattern are formed on the peripheral edge of the substrate, and therefore the resist film is removed in an area of about several millimeters from a substrate side surface, so that a pattern defects of the alignment mark and the QA pattern do not occur.